Your app sucks, give me a refund!
Developers don't see who bought their apps and have no means to send money back to users - the purchase process is completely under Apple's control. To get a refund, you need to do it through Apple's web interface or iTunes. Check for instance this article for more information:
Please let me know what I could do better - "your app sucks" type of feedback is useless. I'm always interested in suggestions how to improve the app. I'm unfortunately limited in what I can do under iOS so please search the Knowledge Base first as not everything is possible.